How does Analytics and Usability software do this?

I have been using analytics software for a while, and I've been asking myself how can such software copy a webpage completely to then place it in an iframe and overlay it with images and info.

An example:

A major problem I encountered is cop开发者_JAVA百科ying the webpage.

In particular, copying the webpage the user is currently viewing! (account panel, form journeys, etc...)

I guess this could be achieved by sending the html with the usability data, but I see this as a major performance problem...

Any comments on the subject? This would be very interesting! =)

Further findings:

• I discovered that sending the HTML over GET, could be made mode efficient by using client-side compression. Although I'm still not 100% convinced by this!

I think they don't actually copy the whole page for your visitors, all of what they need, is to track the mouse location (x and y coordinates) and a url of the current page being shown,

then they will make use of these information to show you all kind of information (where the user was looking, what have been clicked, ... etc).

AFAIK the google analytics "hot links" widget doesn't copy the page at all -- it just shows it in an iFrame with stuff overlaid on it. (in google analytics' case, they can also modify the page display by sending instructions to the analytics JS embedded in the page.)

The above looks like a whole different kettle of fish though -- you sure it is html and not a screenshot?